/**
 * bem helper
 * b() // 'button'
 * b('text') // 'button__text'
 * b({ disabled }) // 'button button--disabled'
 * b('text', { disabled }) // 'button__text button__text--disabled'
 * b(['disabled', 'primary']) // 'button button--disabled button--primary'
 */

export type Mod = string | { [key: string]: any };
export type Mods = Mod | Mod[];

/**
 * @description: 根据元素名称生成对应的名称
 * @param {string} name 元素名称
 * @param {Mods} mods
 * @return {String}
*/
function gen (name: string, mods?: Mods): string {
  if (!mods) {
    return ''
  }
  
  if (typeof mods === 'string') {
    return ` ${name}--${mods}`
  }
  
  if (Array.isArray(mods)) {
    return mods.reduce<string>((ret, item) => ret + gen(name, item), '')
  }
  
  return Object.keys(mods).reduce(
    (ret, key) => ret + (mods[key] ? gen(name, key) : ''),
    ''
  )
}

/**
 * @description: 创建块元素
 * @param {string} name 块名称
 * @return {Function} 
 */
export function createBEM (name: string) {
  return function (el?: Mods, mods?: Mods): Mods {
    if (el && typeof el !== 'string') {
      mods = el
      el = ''
    }
    
    el = el ? `${name}__${el}` : name
    
    return `${el}${gen(el, mods)}`
  }
}

export type BEM = ReturnType<typeof createBEM>;
